Marrow transplantation is the only treatment which can consistently produce long-term disease-free survival in patients with CML. In this subproject we will attempt to improve the prospects for long-term disease-free survival in all phases of the disease. This will be accomplished by evaluating in randomized trials more intensive treatment regimens. Phase I-II treatment trials will be carried out in patients in the accelerated or blastic phases of CML. We will study the timing of marrow transplantation as it relates to phase and other prognostic parameters. We will also study patterns of leukemic relapse by using the Ph marker and other polymorphisms in an effort to uncover the relationship between split chimerism, rejection and relapse.